export const BILLING_STATUS_VALUES = ["paid", "partial", "pending", "overdue"] as const;
export type BillingStatus = (typeof BILLING_STATUS_VALUES)[number];

export const BILLING_STATUS_LABELS: Record<BillingStatus, string> = {
  paid: "已结清",
  partial: "部分收款",
  pending: "待收款",
  overdue: "已逾期",
};

export const PAYMENT_METHOD_VALUES = ["wechat", "alipay", "bank_transfer", "card", "cash"] as const;
export type PaymentMethod = (typeof PAYMENT_METHOD_VALUES)[number];

export const PAYMENT_METHOD_LABELS: Record<PaymentMethod, string> = {
  wechat: "微信支付",
  alipay: "支付宝",
  bank_transfer: "银行转账",
  card: "银行卡",
  cash: "现金",
};

export const INVOICE_STATUS_VALUES = ["not_requested", "pending", "issued"] as const;
export type InvoiceStatus = (typeof INVOICE_STATUS_VALUES)[number];

export const INVOICE_STATUS_LABELS: Record<InvoiceStatus, string> = {
  not_requested: "未开票",
  pending: "待开票",
  issued: "已开票",
};

export type BillingCharge = {
  id: string;
  category: string;
  description: string;
  quantity: number;
  serviceDate: string;
  unitPriceCents: number;
};

export type BillingPayment = {
  id: string;
  amountCents: number;
  method: PaymentMethod;
  paidAt: string;
  reference: string;
  operator: string;
  note: string;
};

export type BillingStatement = {
  id: string;
  elderId: string;
  elderName: string;
  roomLabel: string;
  contactName: string;
  contactPhone: string;
  period: string;
  dueAt: string;
  charges: BillingCharge[];
  payments: BillingPayment[];
  invoiceStatus: InvoiceStatus;
  invoiceNumber?: string;
  receiptCount: number;
};

export type BillingStatementView = BillingStatement & {
  totalCents: number;
  paidCents: number;
  outstandingCents: number;
  status: BillingStatus;
};

export type BillingSummary = {
  receivableCents: number;
  collectedCents: number;
  outstandingCents: number;
  overdueCount: number;
};

export function getChargeAmountCents(charge: BillingCharge): number {
  return Math.round(charge.quantity * charge.unitPriceCents);
}

export function getStatementTotalCents(statement: BillingStatement): number {
  return statement.charges.reduce((total, charge) => total + getChargeAmountCents(charge), 0);
}

export function getStatementPaidCents(statement: BillingStatement): number {
  return statement.payments.reduce((total, payment) => total + payment.amountCents, 0);
}

export function getStatementOutstandingCents(statement: BillingStatement): number {
  return Math.max(0, getStatementTotalCents(statement) - getStatementPaidCents(statement));
}

export function getBillingStatus(statement: BillingStatement, referenceDate = new Date()): BillingStatus {
  const outstandingCents = getStatementOutstandingCents(statement);
  if (outstandingCents === 0) {
    return "paid";
  }

  if (new Date(statement.dueAt).getTime() < referenceDate.getTime()) {
    return "overdue";
  }

  return statement.payments.length > 0 ? "partial" : "pending";
}

export function toBillingStatementView(
  statement: BillingStatement,
  referenceDate = new Date(),
): BillingStatementView {
  const totalCents = getStatementTotalCents(statement);
  const paidCents = getStatementPaidCents(statement);
  return {
    ...statement,
    totalCents,
    paidCents,
    outstandingCents: Math.max(0, totalCents - paidCents),
    status: getBillingStatus(statement, referenceDate),
  };
}

export function calculateBillingSummary(
  statements: readonly BillingStatement[],
  referenceDate = new Date(),
): BillingSummary {
  return statements.reduce<BillingSummary>(
    (summary, statement) => {
      const view = toBillingStatementView(statement, referenceDate);
      return {
        receivableCents: summary.receivableCents + view.totalCents,
        collectedCents: summary.collectedCents + view.paidCents,
        outstandingCents: summary.outstandingCents + view.outstandingCents,
        overdueCount: summary.overdueCount + (view.status === "overdue" ? 1 : 0),
      };
    },
    { receivableCents: 0, collectedCents: 0, outstandingCents: 0, overdueCount: 0 },
  );
}

export function addBillingPayment(statement: BillingStatement, payment: BillingPayment): BillingStatement {
  return {
    ...statement,
    payments: [payment, ...statement.payments],
  };
}

export function addBillingCharge(statement: BillingStatement, charge: BillingCharge): BillingStatement {
  return {
    ...statement,
    charges: [...statement.charges, charge],
    invoiceStatus: "not_requested",
    invoiceNumber: undefined,
  };
}

export function formatCny(cents: number): string {
  return new Intl.NumberFormat("zh-CN", {
    style: "currency",
    currency: "CNY",
    minimumFractionDigits: 2,
  }).format(cents / 100);
}

export function formatBillingPeriod(period: string): string {
  const [year, month] = period.split("-");
  return year && month ? `${year}年${month}月` : period;
}